1. Field Of The Invention
This invention relates to a method for expanding the volume of tobacco by first adsorbing volatile substances thereon followed by condensation and absorption to substantially fill the mesoporous spaces thereof, thus allowing diffusion into the closed cellular spaces to provide a propellant, and subsequently heating the diffused propellant to expand the tobacco.
2. Description of the Prior Art
The reconstitution of dried tobacco products has been long practiced in the tobacco industry. In U.S. Pat. No. 3,144,871 it was recognized that tobacco could be partially restored to its predried volume by exposing it for a period of time to organic solvent vapors and subsequently allowing the solvent to evaporate. U.S. Pat. Nos. 3,524,451 and 3,534,452 taught the impregnation with liquid solvents under pressure followed by expansion in a high temperature gas stream, resulting in the doubling of the volume of the tobacco. As an alternative to impregnation with liquids or vapors, tobacco can be expanded with gases, as recognized in U.S. Pat. No. 1,789,435 or by means of solid compounds which decompose to form gases such as in U.S. Pat. No. 3,771,533.
The initial developments in the tobacco expansion process were performed in relatively unsophisticated laboratory apparatus or, on a commercial scale, with equipment described as readily available or easily modified by processes generally simple and straightforward. Improvements were obtained by the employment of volumes or weights of impregnating materials equal to that of the tobacco and resorting to extremes of process temperatures and pressures. These processes have subsequently been the subject of extensive study and refinement over the intervening years, with increases in performance and economy. Such developments have resulted in economic advantages in volume but at substantial increases in costs and with considerable detriment to tobacco quality, such that the quantity of expanded tobacco utilized has not exceeded 10-30% in products due to a combination of economic and organoleptic limitations. Most recently, the use of chlorofluorocarbons, which forms the basis of the certain prior processes, has been banned and commercial practice is now centered on processes which employ CO.sub.2.
Former expansion processes are no longer ecologically acceptable and most existing processes are capital and energy intensive, destructive of the organoleptically and chemically desirable tobacco properties and add an ecological burden to the environment. Beyond simple economics, an additional and growing incentive for minimum weight tobacco products is the "ignition propensity" of cigarettes which is a cause of great concern to both the manufacturer and consumer.